1. Field of the Invention
This application relates generally to steering columns, and more specifically, to applying a resultant force required to resist collapse of a collapsible steering column during an emergency condition.
2. Description of Related Art
Automotive steering columns are typically collapsible and equipped with kinetic energy absorption devices that employ some device to create a resultant or resisting force to the collapse of the steering column. The resultant force reduces injury to a vehicle operator caused by the operator impacting a steering wheel as a result of an emergency condition, i.e., a collision. Such impacts during vehicle collision typically cause the steering column to collapse and a resultant force by resisting the collapse of the steering column absorbs the energy transmitted through the steering column.
Such collapsible steering column assemblies generally include a column that translates linearly and collapses during the emergency condition. A force generated by the driver impacting the steering wheel initiates the collapse by releasing the column. The column moves against the resultant force that may be produced by an energy absorption device designed to convert a portion of the driver's kinetic energy into work. The resultant force may be generated by systems including a plastically deformable metal element incorporated into the energy absorbing device. Such energy absorbing devices have a set resultant force or fixed energy absorption capability, and offer no control to vary the absorption capability over their performance during the collapse of the steering column assembly. More specifically, traditional energy absorbing devices have a fixed resultant force which is optimized to protect a given and limited group of drivers. In most cases the group represents an average size male driver.
In order to provide some adjustability at the initial determination of the emergency condition or collapse of the steering column, devices have been developed to produce a stage-variable resultant force. Typically, these devices utilize a pyrotechnic device incorporated into the collapsible steering column assembly. The pyrotechnic device selectively engages any number of a plurality of energy absorption devices disposed within the steering column assembly. Such a steering column assembly is disclosed in U.S. Pat. No. 6,578,872 to Duval et al. Steering column assemblies including the pyrotechnic devices allow for the energy absorption curve of the resultant force to be customized to match for example attributes of the driver and the severity of the emergency condition. However, variability of the energy absorption curve or the resultant force is based on engaging zero, one, two, etc. energy absorption devices disposed within the steering column assembly. The amount of energy absorbed by each individual energy absorption device does not vary. A variation in the absorption curve is achieved by changing the number of absorption devices utilized during the emergency condition. In addition, the pyrotechnic devices offer no variability to the energy absorption curve or the resultant force needed to collapse the steering column after the initiation of the emergency condition and the activation of the pyrotechnic device. Therefore, the pyrotechnic devices can not compensate or adjust the resultant force throughout the collapse of the steering column during the emergency condition.
Accordingly it would be desirable to develop a device that can apply and vary a resultant force needed to collapse the steering column assembly during the emergency condition and through out an entire emergency condition.